gcc@6: deprecate

Closes #110163.

Signed-off-by: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Signed-off-by: Michka Popoff <3406519+iMichka@users.noreply.github.com>
Signed-off-by: BrewTestBot <1589480+BrewTestBot@users.noreply.github.com>

Formula/gcc@6.rb

@@ -10,11 +10,6 @@ class GccAT6 < Formula
   ]
   revision 7
 
-  livecheck do
-    url :stable
-    regex(%r{href=.*?gcc[._-]v?(6(?:\.\d+)+)(?:/?["' >]|\.t)}i)
-  end
-
   bottle do
     rebuild 1
     sha256                               monterey:     "6c06fbf374a3d102b63992b16c4d4af3e1631db7a6b7a73663de40abdbee276f"
@@ -27,6 +22,9 @@ class GccAT6 < Formula
   # out of the box on Xcode-only systems due to an incorrect sysroot.
   pour_bottle? only_if: :clt_installed
 
+  # https://gcc.gnu.org/gcc-6/
+  deprecate! date: "2022-09-09", because: :deprecated_upstream
+
   depends_on arch: :x86_64
   depends_on "gmp"
   depends_on "isl"